1. Field of the Invention
This invention relates to a novel optical transceiver for use in measurement, evaluation and correction of optical density of a surface having toned images, more specifically, to the measurement of reflectance of radiation from a toned image surface and to the assignment of correct optical density to the measurement of toned images.
2. Background of the Invention
It is often useful to print large quantities of multi-colored prints to paper for the purpose of disseminating multiple copies of reports or brochure information. One objective of this kind of printing is to assure that all of the reports or brochures look the same, which means that the printing of each of the colors in multi-color pages and the color or shade of black in monochrome pages must maintain a consistent density as printing progresses. It is not desirable to allow the densities of primary colors to vary from page to page because the value and quality of the final product of the reports and/or brochures will be degraded if the colors are varying from document to document. Therefore, measuring density of images (i.e., plated toner) during the printing process is important.
There have been many attempts made to achieve the above objective in the printing process or electrophotographic applications. For example, in U.S. Pat. No. 5,533,139 to Parker et al., a method has been disclosed for detecting coating density imperfections. A light is transmitted through a substrate that is to be inspected, and then significant image processing is applied to make decisions. A quadrifurcated fiber optic bundle has been used with annular illumination techniques so that incident radiation upon the sample is introduced at an angle to the collecting fiber optic axis, as disclosed in U.S. Pat. No. 4,947,348 to Van Arsdell. This disclosure implies that if the surface of the test piece exhibits a large component of specular reflection, then the illuminating radiation will reflect out of the collecting aperture. This kind of annular illumination is good for diffuse surfaces such as paper, but will not work for specular surfaces like polished metal or a photoconductor surface. Moreover, in the disclosed apparatus, all four of the quadrifurcated optical bundle channels are dedicated to detection of radiation and none are used to introduce radiation into the test piece. The annular illuminators are quite large in diameter compared to the fiber bundle and might therefore mechanically interfere with the system being observed.
Another attempt to determine coating density imperfections is disclosed in U.S. Pat. No. 4,950,905 to Butler. This reference uses diffrimoscopic imaging that intentionally throws away directly reflected light and analyzes the diffusely reflected and/or scattered light to make decisions. Not only does this arrangement require a lot of space to set up, but also the signals from diffuse reflection and scattering are weak compared to the specularly reflected component. Consequently this system needs very high quality, high gain amplifiers to function properly.
Bifurcated optical fibers are frequently used in sensors to detect a distance to a target. Typically, one sensor bundle comprises two sets of fibers, each set of fibers originating from a respective branch, the two sets of fibers being joined in a common end. Light is transmitted from a light source through one branch to the target and the corresponding light reflected from the target is conducted by the other branch to a light sensor. The intensity of the reflected light is indicative of the distance between the end of the common branch and the target.
There is a present need for diminutive and inexpensive apparatus and a measurement method capable of indicating the optical density of the toned images on the surface of a substrate, yielding reliable, consistent and accurate results in different applications, including electrophotography.